1. Field of the Invention
The present invention generally relates to an image forming apparatus including an image carrier, and particularly to cleaning control of an image carrier.
2. Description of the Related Art
In an image forming apparatus that uses a transfer method that adopts an electrophotographic process or an electrostatic recording process, it is necessary to clean developer that is not transferred to a paper sheet and remains on the surface of an image carrier. If an image carrier and a cleaning blade are left in a state of contact against each other, finely-powdered toner or an additive agent or the like aggregates at the contact regions. These aggregates may cause image defects such as streaks or image blurring (density fluctuations and the like). In general, a friction coefficient μ at a portion at which finely-powdered toner and the like is aggregated on the surface (circumference) of the image carrier decreases relatively. Hence, when a cleaning blade passes through a portion at which the friction coefficient μ has decreased, the rotational speed (circumferential speed) of the image carrier temporarily increases. This is one cause of image defects such as streaks and image blurring.
Japanese Patent Laid-Open No. 2005-062280 discloses an invention that reduces aggregates by stopping an image carrier when image formation ends, and thereafter removing finely-powdered toner by performing microscopic rotation of the image carrier and, furthermore, counter-rotating the image carrier. Japanese Patent Laid-Open No. 2006-091685 discloses an invention that intermittently rotates an image carrier in the same direction as the rotational direction at the time of image formation, and thereafter rotates the image carrier in the opposite direction.
The inventions disclosed in Japanese Patent Laid-Open No. 2005-062280 and Japanese Patent Laid-Open No. 2006-091685 offer excellent advantages with respect to reducing image defects such as streaks and image blurring caused by aggregates such as finely-powdered toner or additive agents by moving the surface (circumference) of the image carrier a predetermined distance after the image carrier has stopped. However, there is a new demand for decreasing operational sounds emitted from a portion at which an image carrier and a cleaning blade contact or from a motor drive gear train or the like when cleaning the image carrier. In this case, the term “operational sound” refers to a sound that is generated in response to driving of an image carrier in a cleaning sequence.
In particular, since a color image forming apparatus includes a plurality of image carriers, operational sounds that are significant in an acoustic sense are liable to occur when the plurality of image carriers are cleaned at the same time. Further, because a cleaning sequence for cleaning is executed after image formation, the discomfort index with respect to a user is liable to increase. The reason is that, although a user is likely to tolerate operational sounds that relate to image formation, there is a tendency for a user to consider an operational sound that has little relevance to image formation as a discomfort. In this case, the term “acoustic sense” refers to a state in which any kind of sound is audible to the human ear. Hence, it is not the case that the physical magnitude of a sound (magnitude of vibrational energy) always corresponds to the magnitude of a sound that is perceived by a human.